Nitration processes

ABSTRACT

The present invention relates to improvements in processes of preparing dinitrated .[.aromatic compounds, particularly dinitrated aniline and dinitrated substituted aniline compounds, employing relatively dilute and then more concentrated nitric acid as the nitrating agent.]. .Iadd.aniline and substituted phenol compounds in a two-step process, employing, in the first or mononitration step the spent nitric acid from the second of dinitration step. .Iaddend.

TECHNICAL FIELD

The present invention relates to improvements in processes for preparingdinitrated aromatic compounds, particularly aromatic compounds such asaniline and substituted aniline compounds, employing relatively diluteand then more concentrated nitric acid as the nitrating agent. Moderatereaction temperatures are used. In these processes two nitro groups areintroduced in the benzene or aromatic ring of the compound to benitrated.

BACKGROUND ART

It has been common practice in the past in the preparation of dinitroaromatic compounds to use concentrated nitric acid containing sulfuricacid as a catalyst, as the nitrating medium. This is as exemplified, inU.S. Pat. No. 4,136,117 to Robert E. Diehl and Stephen D. Levy, issuedJan. 23, 1979. Also it is known from the same patent (col. 1, lines52-60) that Belgium Pat. No. 762,232 discloses a method for thepreparation of 2, 6-dinitro-tertiary anilines, wherein bothN-substituents are haloalkyl, by nitration with at least a five foldexcess of nitric acid, which is present at the start of the reaction ina concentration of 50% to 90% and in an amount to leave an acidconcentration of 50% at the end of the reaction, in the presence of acatalytic amount of nitrous acid or nitrite ion generating material.

Each of the above processes have disadvantages from an economical andenvironmental standpoint. The processes utilizing mixtures of nitricacid and sulfuric acid generate spent acids containing 40% or more acid,including some nitric acid. This spent acid either has to be neutralizedprior to disposal--resulting in the generation of considerable amountsof mixtures of sodium nitrate and sodium sulfate which must be disposedof in the environment--or the spent acid must be concentrated byevaporation of water (with expenditure of energy) to a concentrationwhich can be used for subsequent nitration reactions.

In the other process, referred to above, in which a five fold excess ofconcentrated nitric acid is utilized along with a nitrous acid ornitrite ion generating material, the spent acid from the dinitrationprocess contains 50% or more of nitric acid. This spent acid, like thatcontaining sulfuric acid, must either be concentrated prior to use inthe dinitration process or must be neutralized, for example, to formsodium nitrate, and then disposed of in the environment.

DISCLOSURE OF THE INVENTION

The present invention has, as one object, the elimination or minimizingof the above described disadvantages. In accordance with the presentinvention, the first nitro group is introduced into the aromaticcompound, for example, aniline or phenol, by reacting such compound atmoderate temperature and pressure conditions, for example, about 40°-65°C. and atmospheric pressure, with a relatively dilute aqueous nitricacid of the order of 10%-50% by weight HNO₃ concentration in thepresence of a suitable liquid, water-immiscible organic solvent for thenitratable compound; for example, a solvent such as dichloroethane. Inthe case of aniline, the compound formed is either mononitroaniline or areaction product of aniline and nitric acid which is believed to be asalt of aniline and nitric acid. In the case of phenol, the compoundformed is mononitro phenol. The resulting mixture is then allowed toseparate into an organic phase containing such solvent and the nitratedaromatic compound and a water phase which contains 10% by weight or lessof HNO₃.

Next the nitratable aromatic compound in the organic phase is reactedwith a relatively concentrated aqueous nitric acid of about 60%-100% byweight HNO₃ concentration at moderate temperature and pressureconditions, for example, of the order of 40°-70° C. and atmosphericpressure. In this reaction the aromatic compound is dinitrated, that is,two nitro groups are introduced into the aromatic ring of the compound.In the case of phenol, a dinitro phenol is formed and in the case ofaniline, the reaction results in the formation of the dinitroaniline.The spent (more dilute) acid from this step can then be reacted withaniline as described in the first step above.

Although reference has been made above to the reaction of nitric acidand aniline, the processes of this invention are also applicable to thedinitration of nitratable aromatic compounds in general, and tosubstituted anilines, phenol and substituted phenols in particular, aswill be described in greater detail hereafter.

The processes of this invention are carried out using nitric acid whichis substantially free of sulfuric acid, but which may be free of or maycontain catalytic amounts on nitrous acid or nitrite ion generatingmaterial. It is preferred to use pure or technical grade nitric acid asmade and sold commercially as the nitrating agent in the second step,and free from additives or catalytic additives.

THE DRAWINGS

The accompanying drawing, FIG. 1, is a flow diagram which is a schematicrepresentation of equipment which can be used to carry out one of thepreferred embodiments of the processes of this invention involving thedinitration of substituted aniline compounds.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, numerals 10, 11 and 12 represent, respectively, storage tanksfor the liquid organic solvent, liquid nitric acid, and the liquidsubstituted aniline compound to be dinitrated in the process. By meansof one of the pumps 9, pipe line 13, connected to tank 10, conveyssolvent from storage tank 10 to solvent extractor 14. Pipe line 15,connected to tank 12, similarly conveys the substituted aniline fromstorage tank 12 to the reactor 16, for reaction with a dilute or spentnitric acid from a source to be described below. The reaction mixtureoverflow from reactor 16 flows via pipe line 17 to a separator 18 inwhich the substituted aniline-nitric acid reaction product (alsoreferred to as aniline salt) is separated from the aqueous phase of thereaction mixture as a lower layer which can flow via pipe 19 to areaction vessel 20 (designated Reactor I). Concentrated nitric acid isconveyed to vessel 20 via pipe 21 from storage tank 11. Dinitration iscarried out in vessel 20 and vessel 22 (designated Reactor II) whichprovide sufficient dwell time to insure that a dinitrated product isobtained; the reaction mixture in vessel 20 overflows from that vesselthrough pipe 23 to vessel 22 where additional dwell time is provided.The overflow from vessel 22 flows through pipe line 24 to separator 25in which the dinitrated product is allowed to separate from the aqueousspent nitric acid. This spent acid is then pumped through pipe 26 toreactor 16 for reaction with additional substituted aniline.

The upper layer (aqueous phase) in separator 18 flows via pipe 27 to thesolvent extractor 14 and the overflow from this extractor flows via pipe28 to separator 29 wherein the solvent and aqueous phase are allowed toseparate into an upper aqueous phase, which is waste, and a solventlower phase which solvent phase is pumped via pipe line 30 to reactor16.

There is also provided, in FIG. 1, pipe line 31 which is connected toorganic solvent pipe line 13 and permits solvent to be pumped fromstorage tank 10 to reactor 22 (Reactor II), if required. In addition,pipe line 32 is provided to convey nitric acid, if required, from pipeline 21 (connected to storage vessel 11) to reactor 16.

As is indicated in FIG. 1 alll reaction vessels 16, 20 and 22 areprovided with cooling coils and agitators to provide temperature controland intimate mixing of the vessel contents, and also with condensers tocondense vapors back into the reactors. Conventional valves are used asshown in the drawing.

As noted above, the present invention is practiced in several steps, oneof which comprises reacting a dinitratable aromatic compound, forexample, aniline or a substituted aniline, with an aqueous dilute orspent nitric acid (from another step as described hereinafer) of about20%-50% by weight .[.HNO'hd 3.]. .Iadd.HNO₃ .Iaddend.in the presence ofa suitable liquid, water-immiscible organic solvent. In most instancesthe mole ratio of nitric acid to aromatic compound is about 1:1 to about18:1, preferably about 1:1 to about 1.5:1. This step is generallycarried out at atmospheric pressure of the order of about 700-790millimeters of mercury and at moderate temperatures of the order of40°-70° C. These temperatures are maintained by cooling the reactants,if necessary. Generally cooling is necessary.

In the following description the term "an .[.aniline'38.]..Iadd.aniline" .Iaddend.is intended to include aniline or a substitutedaniline, and the substituted aniline can be N-substituted, that is, haveone or two substituent groups instead of hydrogen or the nitrogen atomor can be ring substituted, or both.

Any dinitratable aromatic compound can be used in the present process. Aparticularly suitable class of dinitratable aromatic compounds which canbe used are aniline, and substituted anilines of the following FormulaI: ##STR1## wherein: Y is hydrogen, halogen, alkyl C₁ -C₄, alkenyl C₂-C₄, --CN, --SO₂ NR₃ R₄ or CF₃ ;

Z is hydrogen, alkyl C₁ -C₄, alkenyl C₂ -C₄, or mono-substituted alkylC₁ -C₄ where the substituent can be halogen, alkoxy C₁ -C₄ or --N--R₃ R₄;

R₁ is hydrogen, alkyl C₁ -C₆, alkenyl C₂ -C₆ or alkynyl C₂ -C₆ ;

R₂ is aklyl C₂ -C₇ (straight, branched or cyclo), alkenyl .[.C₂ 14 C₆.]. .Iadd.C₂ -C₆ .Iaddend., alkynyl C₂ -C₆, or mono-substituted alkyl C₁-C₄ where the substituent is halogen or alkoxy C₁ -C₄ ;

R₃ and R₄ each are hydrogen or alkyl C₁ -C₄ and when R₁ and R₂ are takentogether they represent piperidino, pyrolidino or morpholino.

Illustrative of substituents falling within the above definition arethose described in U.S. Pat. No. 4,165,231 (column 1, lines 53-65)issued on Aug. 21, 1979, to Albert W. Lutz and Robert F. Piehl, whichdescription is hereby incorporated herein by reference. Illustrative ofcompounds falling within the above Formula I are the non-nitratedcompounds described in columns 3 and 4 of the same patent, that is, thecompounds described in these columns but which have no nitrosubstituents. Such compounds are hereby incorporated herein byreference.

Preferred substituted aniline compounds for dinitration within the scopeof Formula I are those of the following Formula II: ##STR2## wherein, R₇is CH₃, C₂ H₅, C₃ H₇ --n, C₃ H₇ --i, C₄ H₉ --i, CF₃ or Cl,

X is CH₃, CH₂ --O--CH₃ or --CH(CH₃)OCH₃ ; and

R₅ is CH₃ -C₇ secondary alkyl, or monochloralkyl C₃ -C₄.

The 2, 6 dinitro derivatives of the substituted aniline compounds withinthe scope of Formula II are stated to be preemergence herbicides in theabove U.S. Pat. No. 4,165,231, except for the excitation referred to insaid patent.

The preferred substituted aniline compounds to be dinitrated inaccordance with the present invention are N-sec-butyl-3, 4-xylidine,N-(1-ethylpropyl)-3, 4-xylidine and N-(1-methylbutyl)-3, 4-xylidine.

Another suitable class of aromatic compounds which can be dinitrated inaccordance with the present invention are phenol or substituted phenolsof Formula III below: ##STR3## wherein R₆ is hydrogen, alkyl C₁ -C₁₂,alkoxy C₂ -C₆, halosubstituted alkyl C₁ -C₁₂, or alkylalkoxy C₃ -C₈ ;

R₉ is alkyl C₁ -C₆, alkoxy C₂ -C₆, halosubstituted alklyl C₁ -C₆,hydrogen, halogen, amino or substituted amino;

R₈ comprises the same substituents as U; and

T comprises the same constituents as U and V with the further provisothat if both U and V are other than hydrogen then T is hydrogen.

Illustrative alkyl substituents when alkyl is C₁ -C₆ are methyl, ethyl,n-propyl, iso-propyl, n-butyl, t-butyl, pentyl, sec. butyl, 2-pentyl andthe like, and when alkyl is C₁ -C₁₂ the foregoing substituents plusn-octyl 2-octyl, 6-octyl, 2-propylhexyl, decyl, dodecyl and the likelike.

Illustrative of C₁ -C₆ alkenyl substituents are ethenyl, 1-propenyl,2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-hexenyl and the like.

The preferred phenols for use in the dinitration processes of thepresent invention are phenol, o-cresol, o-secbutyl phenol, octyl phenol,decyl phenol and dodecyl phenol, and these compounds fall within thescope of Formula III when U and V are hydrogen and R₆ is one of theabove named substituent groups or in the case of o-cresol, T is methyland U, V and R₆ are hydrogen.

As previously noted above, when an aniline is reacted with the spentnitric acid, the reaction product can be a mononitrated product or thereaction product of an aniline and nitric acid, which for convenience issometimes referred to herein as an aniline salt. Whether the reactionproduct is mononitrated or such salt will depend on the particularsubstituted aniline compound used, the concentration of the spent nitricacid employed and the mole ratio of HNO₃ to aniline compound. Ingeneral, if the aniline compound used falls within the scope of FormulaI or II and the concentration of the spent nitric acid is about 10%-40%by weight of HNO₃ and the mole ratio is about 1:1 to about 1.3:1, ananiline salt is formed. With such spent acid concentration and compoundswithin the scope of Formula I, in most instances an aniline salt will beformed. With higher spent acid concentrations, the reaction product willusually be the mononitro derivative of the aniline or substitutedaniline compound. This is usually also the case if the spent acidconcentration is about 35% and the HNO₃ to aniline mole ratio is above1.3:1.

There is a considerable advantage in forming an aniline salt in that thesubsequent reaction thereof with concentrated nitric acid to form thedinitro derivative proceeds quickly and smoothly, and with the formationof a spent nitric acid concentration for use in reaction with additionalsubstituted aniline. Moreover, the generation of a spent acid which canbe used for an aniline salt formation results in a nitric acid recycleoperation in which comparatively very little nitric acid must beneutralized, concentrated or discarded, in contrast to prior practice.The spent nitric acid concentration required to form an aniline salt canbe quite low, for example, 10% by weight HNO₃, and when such salt formsit is quite soluble in the organic solvent used and separatesessentially completely from the aqueous phase containing any residualnitric acid which can be 1% by weight HNO₃ or lower. This is the onlynitric acid waste generated in the process. The resulting aniline saltis then dinitrated as described below.

There also be thermodynamic advantages in the processes of thisinvention in which an aniline is to be dinitrated and an aniline salt isformed using spent nitric acid of the concentrations herein described,as compared to a standard straightforward nitration. In the latter typeof nitration, either batch or continuous, an aniline is mixed with theconcentrated nitrating acid to form the dinitro aniline and water, witha heat of reaction of the order of -30 Kcal/gram mole for each NO₂ groupadded. During the reaction, all of this heat must be removed by cooling,with the exception of the heat used to raise the temperature of thereactants to reaction temperature.

In contrast, when an amine salt is formed first and then reacted withconcentrated nitric acid to form the dinitrated product, as in thepresent process, there is a division of reactions and therefore adivision of heats. Thus, when an aniline in a solvent is reacted withspent or dilute nitric acid of about 20%-25% by weight HNO₃concentration, the heat of aniline salt formation is just about enoughto raise the temperature of the reaction mixture to about 60° C. or thedesired temperature. Consequently no heating or cooling are required.When the aniline salt in the solvent is then reacted with moreconcentrated HNO₃, the heat of dinitration is approximately the same asin the standard straightforward dinitration but in contrast thereto,another reaction must take place, namely, aniline salt dissociation.This dissociation is the reverse reaction of the salt formation andtherefore is endothermic, taking up about as much heat as the saltformation process gives off. This is true whether the salt dissociationtakes place before, as is probably the case, or after the dinitrationreaction. It can be seen from the foregoing that, in the aniline saltformation process and dinitro group introduction into the anilinecompound, the heat of formation or reaction of about one NO₂ group iseliminated in contrast to the standard dinitration, and this results inthe elimination of a very high heat load in the first stage reactor ofthe dinitration process. Stated differently, only half the usual coolingis required, thus saving energy, and the danger of hot or runawaynitration reactions is substantially reduced.

When phenol or substituted phenols are nitrated in accordance with thepresent invention, the reaction product with the spent nitric acid(about 34%-50% HNO₃ by weight) is a mononitrophenol, primarily2-nitrophenol and 4-nitrophenol, or 2-nitro substituted phenol or4-nitro substituted phenol. There is no phenol nitric acid saltformation, as in the case of substituted anilines as described above,unless the phenol contains amino or substituted amino groups on thebenzene ring.

In practicing another or second step of the present process, themononitro derivative of the aromatic compound, such as phenol or ananiline salt, prepared as described in the above discussion anddissolved in the organic solvent phase of the first step, is reactedwith a more concentrated aqueous nitric acid. As noted previouslyherein, the nitric acid concentration is about 60%-100% by weight ofHNO₃, and is preferably 65%-75% by weight of HNO₃. This reaction iscarried out at moderate temperature and pressure conditions, that is,temperatures of about 40°-70° C., preferably 50°-65° C., and pressuresof the order of 700-790 millimeters of mercury. These pressurescorrespond essentially to prevailing or ambient atmospheric pressures.

In carrying out this dinitration (second) step, the mole ratio of themore concentrated HNO₃ to aniline compound can vary to some extent butis desirably 1.9:1 to 2.5:1, and preferably about 2.0:1 to about 2.3:1,to obtain the advantages of the present invention in reusing theresulting spent nitric acid in the first step of the process, that is,mononitration or aniline salt formation.

As noted above, both nitration steps are carried out in the presence ofa suitable liquid, water-immiscible organic solvent for the aromaticcompound which is being nitrated. A large variety of liquid,water-immiscible solvents can be used but such solvents should besubstantially less reactive to nitric acid than the compound which is tobe dinitrated and are, preferably, inert to or non-nitratable by nitricacid under, the reaction conditions described herein. The relative easeof nitration of various compounds has been described in the literature.By way of illustration, the following is the declining order orreactivity of some compounds with nitric acid: aniline, phenol,mesitylene, xylene, monochlorobenzene (MCB). It is thus possible to usexylene or MCB as the solvent in the reaction if aniline or phenol arebeing nitrated. A particularly suitable class of solvents which can beused and which are inert to nitration under the herein describedreaction conditions are liquid chloro or chloro and fluro derivatives ofsaturated alkanes (straight chain or branched), preferably of 1 to 6carbon atoms. Specific examples of this class of solvents aredichloroethane, trichlorethane, carbon tetrachloride, chloroform and thelike. Dichlorethane is the solvent of choice. The amount of such organicsolvent used should be sufficient to maintain the automatic compound andits various nitrated derivatives formed in the process in solution insuch solvent.

The reaction with more concentrated nitric acid to produce the dinitroderivative of the aromatic compound is allowed to proceed to completionthat is, until two nitro groups are introduced into the aromatic ring ofsuch compound. When the aromatic compound used is aniline or amono-N-substituted aniline, with no ring substitution, the primaryreaction product formed is the 2, 4-dinitro derivative, that is, 2,4-dinitro aniline or the 2, 4-dinitro mono-N-substituted aniline. Therewill also be formed relatively small amounts of the N-nitroso derivativeof such dinitro compounds. When the aromatic compound used is adi-N-substituted aniline, for example, dimethylaniline, the primaryreaction product is also the 2, 4-dinitro derivative, but in the case ofsuch an aniline no nitroso derivative is formed. When the substitutedaniline has substitutent groups in the 3, 4 position, on the benzenering, for example, the dinitro reaction product will be primarily a 2,6-dinitro derivative.

By way of illustration, if the aromatic compound to be dinitrated is amono-N-alkyl substituted 3, 4-alkyl substituted aniline, the reactionproduct is primarily the 2, 6-dinitro derivative and small amounts ofthe N-nitroso derivative. Such derivative can be converted to additional2, 6-dinitro derivative, as will be described in greater detailhereafter.

When the starting aromatic compound is phenol or substituted phenol,with a substituent group on the oxygen atom, the final reaction product,after dinitration, is primarily 2, 4-dinitro phenol or 2, 4-dinitrosubstituted phenol.

The present invention is further illustrated by the following specificexamples which are intended to be illustrative, but not limitative,parts and percentages being by weight unless otherwise specified.

EXAMPLE 1

In the first step, a solution containing 576 grams of dichloroethane and368 grams of 95% N-(1-ethylpropyl)-3, 4-dimethyl aniline (1.83 mole) wasmixed with 328 grams (1.83 mole) of spent aqueous nitric acid of 35.1%HNO₃ concentration at 60° C. for about 30 seconds. The spent acid usedwas obtained in the manner described in the second step of this Example.The mixture was allowed to separate into two (2) phases, that is, anorganic phase and an aqueous phase. The organic phase (almost 1,100grams) contained approximately 576 grams of dichlorethane, 349 grams ofN-(1-ethylpropyl)-3, 4-dimethylaniline combined with 115 grams of HNO₃(the combination is referred to as aniline salt) and 38 grams H₂ O. Theaqueous phase, of about 175 grams, contained less than 1% HNO₃ and lessthan 1% of the aniline compound.

In the second step, the organic phase from the first step was mixed with362 grams (4.02 moles) of aqueous 70% HNO₃ at 60° C. The reactionmixture was stirred for one hour and maintained at 60° C. during thatperiod, after which the mixture was allowed to separate into an organicphase an an aqueous phase consisting essentially of 328 grams (1.83mole) of spent aqueous nitric acid (35.1% HNO₃), essentially the same asused in the first step of this Example. The organic phase containedN-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline andN-nitroso-N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline. Thisphase was treated with 27 grams of 32% Hcl and 23.3 grams of sulfamicacid at 100° C. for three hours with occasional venting to maintain thepressure at 15-20 psi. The mixture was allowed to cool to 50° C., duringwhich phase separation occurred. The aqueous phase was discarded and theorganic phase was neutralized with 2% NaOH solution. The aqueous phasewas separated and the dichlorethane was stripped off under vacuum. Thisresulted in denitrosation of the N-nitroso compound and additional yieldof the desired N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline.

The spent acid of the second step can be used in another first stepreaction.

EXAMPLE 2

In this Example, a reaction similar to that in Example 1 was carried outexcept the spent acid was of higher concentration and mononitration ofthe aniline compound was effected in the first step rather than anilinesalt formation.

In the first step a solution of 368 grams (1.83 mole) ofN-(1-ethylpropyl)3, 4-dimethylaniline in 552 grams of dichlorethane wasmixed with 343 grams of spent aqueous nitric acid of 51.3% HNO₃concentration (2.79 moles) at 60° C. and stirred for one hour. The spentacid used was obtained in the manner described in the second step ofthis Example. The mixture was allowed to separate into two phases, thatis, an aqueous phase and an organic phase, the latter yielding a totalof about 987 grams containing approximately 437 grams of the mononitroderivative of the above mentioned aniline compound and 552 grams ofdichloroethane. The aqueous phase consisted of about 253 grams of 20%HNO₃ concentration.

In the second step, the organic phase from the first step was mixed with434 grams of aqueous nitric acid of 70% HNO₃ concentration (4.82 moles)at 60° C. and the mixture was stirred for one hour while maintaining thetemperature of the mixture at 60° C. by cooling. The mixture was thenallowed to separate into an organic phase and an aqueous phase whichconsisted of about 343 grams of spent aqueous nitric acid of 51.3% HNO₃concentration, essentially the same as used, and usable, in the firststep of this Example. This spent acid can be used per se in anotherfirst step reaction. The organic phase weighing about 1068 grams wascomposed primarily of N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline and minor amounts of N-nitroso-N-(1-ethylpropyl)-3,4-dimethyl-2, 6-dinitro aniline. This phase was treated withhydrochloric acid and sulfamic acid in the same manner as described inthe last paragraph of Example 1 to effect denitrosation of the N-nitrosocompound in the organic phase and thus enhance the yield of desiredproduct N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline.

EXAMPLE 3

The process described in Example 1 was repeated except 172 grams ofaniline (1.83 moles) were used as the starting nitratable materialinstead of N-(1-ethylpropyl)-3, 4-dimethylaniline.

The organic phase obtained in the second step of the process containedessentially 2, 4-dinitro aniline and N-nitroso-2, 4-dinitro aniline. Theaqueous spent nitric acid, obtained in the second step, had a 35% NHO₃concentration. The organic phase was treated with hydrochloric acid andsulfamic acid in the manner described in the last paragraph of Example 1to effect denitrosation of the N-nitroso compound and thus enhance theyield of the desired 2, 4-dinitro aniline.

EXAMPLE 4

This Example pertains to the dinitration of phenol. In the first step asolution of 172 grams of phenol (1.83 moles) and 576 grams ofdichlorethane were mixed with 343 grams of spent aqueous nitric acid of51.3% HNO₃ concentration (2.79 moles) at 60° C. and stirred for onehour. The spent acid used was obtained in the manner described in thesecond step of this Example. The mixture was allowed to separate intotwo phases, that is, an aqueous phase and an organic phase, the lattercontaining primarily a mixture of 2-nitro-phenol and 4-nitro-phenol in576 grams of dichloroethane. The aqueous phase consisted of about 253grams of aqueous spent nitric acid of 20% HNO₃ concentration.

In the second step, the organic phase from the first step was mixed with434 grams of aqueous nitric acid of 70% HNO₃ concentration (4.82 moles)at 60° C. and the mixture was stirred for one hour while maintaining thetemperature of the mixture at 60° C. by cooling. The mixture was thenallowed to separate into an organic phase and an aqueous phase whichconsisted of about 343 grams of spent aqueous nitric acid of 51.3% HNO₃concentration, essentially the same as used in the first step of thisExample. This spent acid can be used per se in another first stepreaction. The organic phase contained essentially all of thedichloroethane employed and dinitrophenol, primarily 2, 4-dinitrophenol.

EXAMPLE 5

The process of Example 4 was repeated except that 197 grams of o-creosol(1.83 moles) was used as the dinitratable aromatic compound instead ofphenol. The aqueous phase obtained on phase separation after conpletionof the second step (dinitration step) contained about 340 grams of spentaqueous nitric acid of 51.5% HNO₃ concentration, essentially the same asused in the first step of this Example. This spent acid can be used perse in another first step reaction. The organic phase obtained on phaseseparation contained essentially all of the dichloroethane employed anddinitro o-creosol.

EXAMPLE 6

In the first step, a solution containing 576 grams of dichloroethane and368 grams of 95% N-(1-ethylpropyl)-3, 4-dimethylaniline (1.83 moles) wasmixed with 574 grams (1.83 moles) of spent aqueous nitric acid of 20%HNO₃ concentration at 60° C. for 30 minutes. The spent acid used wasobtained in the manner described in the second step of this Example. Themixture was allowed to separate into two phases, that is, a lowerorganic phase and an upper aqueous phase. This phase separation was veryclean and sharp, and the two layers were easily separated. The lowerorganic phase (almost 1,100 grams) contained approximately 576 grams ofdichloroethane, 349 grams of N-(1-ethylpropyl)-3, 4-dimethylanilinecombined with 114 grams of HNO₃, the combination being referred to as ananiline salt, and the balance being a small amount of H₂ O. The aqueousphase of about 422 grams consisted of water and less than 1% HNO₃ andless than 1% of the starting substituted aniline compound.

In the second step, the organic phase from the first step was mixed with362 grams (4.02 moles) of aqueous 70% HNO₃ concentration at 60° C. Thereaction mixture was stirred for one hour and maintained at 60° C.during that period. Water was then added to the resulting mixture, whichseparated into a lower organic phase and an upper aqueous (spent nitricacid) phase containing 20% HNO₃ concentration. Because of this phaseinversion, the dinitrated product would be removed at the base of vessel25 and the spent acid removed as overflow, instead of as illustrated inFIG. 1. This spent acid also could be used as the nitrating agent in thefirst step of the process of this Example. The addition of water, asabove, also results in a quenching of the dinitration reaction. Theorganic (lower) phase contained N-(1-ethylpropyl)-3, 4-dimethyl-2,6-dinitro aniline and N-nitroso-N-(1-ethylpropyl)-3, 4-dimethyl-2,6-dinitro aniline. This phase was treated with hydrochloric acid andsulfamic acid in the manner described in the last paragraph of Example 1to effect denitrosation of the N-nitroso compound and thus enhance theyield of the desired N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline.

This Example illustrates the distinct advantages in using spent aqueousnitric acid of 20% or less HNO₃ concentration in the first step of theprocess, in that the aniline salt formed is quite soluble in thedichloroethane organic solvent which enables a sharp separation of theaqueous phase, which is essentially free of nitric acid, from theorganic phase, the dinitration of this aniline compound in the organicphase in the second step with the more concentrated nitric acid thenenables the formation of spent aqueous nitric acid of 35% HNO₃concentration which can, as heretofore described, be used in a firststep reaction with additional aniline compound and thus provides acontinuous recycle procedure. This means that very little nitric acidneed be discarded or concentrated in the entire process.

Further in regard to Example 6, the dilution of the mixture in thesecond step of the process therein and prior to phase separation, notonly quenches the reaction, as is mentioned, but also lowers the densityof the spent acid to a point below that of the dinitratedproduct-solvent phase, thereby causing the spent acid phase to separateto the top and the organic phase to the bottom. In addition, thesolubility of the organic (solvent and dinitro product) constituents ofthe organic phase in the spent acid phase, is significantly lowered thusreducing carry over of these constituents into the spent acid phase.

EXAMPLE 7

The description in this Example is in reference to FIG. 1. Reactor 16 atatmospheric pressure (750 mm of mercury) was supplied with 202 grams ofdichloroethane, 175 grams of N-(1-ethylpropyl)-3, 4-dimethylaniline(hereinafter in this Example referred to as substituted aniline, forconvenience) and 164 grams of spent aqueous nitric acid of 35% of HNO₃concentration, and the contents were maintained at 60° C. To theseparator 18 at atmospheric pressure was added a mixture of 29 grams ofsuch substituted aniline, 44 grams of dichloroethane and 30.28 grams ofthe same spent aqueous nitric acid, all of which were maintained at 60°C. To both solvent extractor 14 and separator 29 were added 570 grams ofdichloroethane and 180 grams of water containing 1% HNO₃. To each of thereactors 20 (Reactor I) and 22 (Reactor II) were added 495 grams of asolution which was 40% N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline and 8% N-nitroso-N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline in dichloroethane to which was added, in each reactor, 238 gramsof spent aqueous nitric acid of 35% HNO₃. The contents of these reactorswere maintained at 60° C. All of the above is simply a way of startingup the continuous process, and the reactors and other equipment usedwere thus filled.

The continuous process was now operated by supplying 6.13 grams/minuteof the substituted aniline, 9.2 grams/minute of dichloroethane and 5.47grams/minute of spent aqueous 35% HNO₃ to reactor 16; and 6.04grams/minute of aqueous 70% HNO₃ to reactor 20. This resulted in anoverflow of emulsion from reactor 16 through pipe line 17 to separator18, where the emulsion separated into an upper aqueous layer and a lowerorganic layer containing the substituted aniline compound-nitric acidsalt and the solvent, which flowed through pipe 19 to reactor 20 towhich the concentrated nitric acid was being supplied with agitation.The overflow from reactor 20 then flowed to reactor 22 through pipe 23.The overflow from reactor 22 then flowed to separator 25 through pipe24. This overflow was an aqueous organic mixture which separated inseparator 25 into an lower phase of aqueous nitric acid of about 35%HNO₃ which was pumped to reactor 16 at the flow rate referred to above(5.47 grams/minute), and an upper organic phase. This upper phasecontained the desired product, namely, N-(1-ethylpropyl)-3,4-dimethyl-2, 6-dinitro aniline, along withN-nitroso-N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline, and wascontinuously withdrawn from separator 25 and treated as hereafterdescribed.

While the foregoing was occurring, the aqueous phase overflow fromseparator 18 was being conveyed to solvent extractor 14 via pipe 27 andconcurrently there was being supplied to the extractor 14, 9.2grams/minute of dichloroethane. The contents of extractor 14 werecontinuously stirred and the overflow from the extractor was conveyed toseparator 29 where the overflow liquid was allowed to separate into anaqueous phase containing about 1% HNO₃ and a lower dichloroethane phasecontaining a low concentration of the substituted aniline. This lower(dichloroethane) phase was pumped back into reactor 16 to supply thedichloroethane to that reactor, as referred to above, at the rate of 9.2grams/minute.

The above process was operated continuously for a 240 minuteequilibration period maintaining the above flow rates and maintainingthe reactor contents at a temperature of 60° C.±1° C. The volume of thesystem was such that 240 minutes equals about four residence times usingthe above flow rates. Then a collection period of 60 minutes ofcontinuous operation was completed during which time the actual totalraw material feeds were:

367.8 grams (1.83 moles) of N-(1-ethylpropyl)-3, 4-dimethylaniline;

362.4 grams (4.03 moles) of concentrated aqueous 70% HNO₃ ;

552 grams of dichloroethane;

328.2 grams (.[.1,83 .]. .Iadd.1.83 .Iaddend.moles) of spent aqueous 35%HNO₃.

The product (organic phase) obtained from separator 25 during the 60minute collection period consisted of 1,068 grams of solution containing438 grams (1.5 moles) of N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline and 78.4 grams (0.24 mole) of N-nitroso-N-(1-ethylpropyl)-3,4-dimethyl-2, 6-dinitro aniline along with dichloroethane. The totalyield of the desired aniline was 95%. There was collected from the loweraqueous layer in separator 25 333 grams of spent aqueous nitric acid of35% HNO₃ concentration, and from the upper aqueous layer in separator 29there was collected 175 grams of aqueous waste of about 1% HNO₃concentration. Denitrosation of the N-nitroso compound in the organiclayer product from separator 25 was effected in the manner described inthe last paragraph of Example 1 to give a yield of the desired productN-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline of 533.7 grams.

It is apparent from this Example that the present process can beoperated continuously to produce a dinitrated product in high yields,and with the generation of very low concentrations of nitric acid wastewhich can be disposed of cheaply and readily.

It will be noted from Example 7 that the continuous processes of thisinvention can be carried out in the following manner. A dinitratablearomatic compound dissolved in an inert organic solvent and diluteaqueous nitric acid of 20%-50% HNO₃ concentration are continuouslysupplied to a reaction zone with agitation and temperature control, aspreviously described above, and in a mole ratio of about 1:1 to about1:1.5 of aromatic compound to HNO₃. The overflow from such zone is thenconveyed continuously to a separation zone to allow the reaction mixtureto separate into an organic phase and an aqueous phase. The organicphase, which contains the organic solvent and reaction product of thearomatic compound and nitric acid, is then supplied continuously toanother reaction zone along with concentrated aqueous nitric acid ofabout 65% to about 80% by weight of HNO₃, with agitation and temperaturecontrol, as previously described above, with sufficient residence timeto complete dinitration of the aromatic compound. In this step, the moleratio of compound to acid suitable for batch operation, as describedabove, is employed in the continuous operation. The reaction mixturefrom this reaction zone is continuously supplied to the separation zonewhere the reaction mixture is allowed to separate into an organic phasecontaining the desired dinitrated aromatic compound and the organicsolvent and an aqueous phase of spent nitric acid containing about20%-50% by weight HNO₃. This aqueous phase is continuously returned tothe first reaction zone for reaction with additional dinitratablearomatic compound. The organic phase is continuously removed from theseparation zone and the organic solvent can be stripped from the desireddinitrated product by vacuum distillation, if desired.

The denitrosation step described in the last paragraph of Example 1, andas referred to in Examples 2, 3, 6 and 7, can be carried out underdifferent and varied conditions as described in the aforementioned U.S.Pat. No. 4,136,117, column 3, lines 47-67; column 4, lines 1-13; column7, Example 16; and column 8, lines 1-23 and Examples 17-24, the subjectmatter of which is hereby incorporated herein by reference.

In the dinitration of anilines, the spent acid resulting from thedinitration step is normally about 35%-40% or from 10%-50% HNO₃. In theprocessing of phenols, the spent acid from the dinitration may be asgreat as 50% HNO₃. To use these acids in the first step of the processesdescribed, they may be substantially diluted, say to 10% concentration.

INDUSTRIAL APPLICABILITY

The present process has wide applicability to commercial processes forpreparation of dinitrated aromatic compounds, including agriculturalherbicides.

I claim:
 1. A continuous process of dinitrating a dinitratablesubstituted aniline compound which comprises continously supplying (1)an aqueous nitric acid of about 10-40% HNO₃ by weight and substantiallyfree of sulfuric acid, (2) a substituted aniline compound and (3) aliquid, inert, water-immiscible organic solvent for said anilinecompound, in a mole ratio of about 1:1 to about 1:1.3 .Iadd.of.Iaddend.HNO₃ to said aniline compound, to a reaction zone at atemperature of about 40° to about 70° C. and atmospheric pressure,thereby forming in said zone an emulsion containing a salt of saidnitric acid and aniline compound, continuously conveying the overflowemulsion from said zone to a separation zone to allow continuousseparation of said emulsion into an aqueous phase and an organic phasecontaining said salt and solvent, continuously conveying said organicphase to a second and third reaction zone and reacting said salt in theorganic phase in said zones with an aqueous nitric acid of 65%-80% byweight HNO₃ and substantially free of sulfuric acid at a temperature ofabout 40° C. to about 70° C. at atmospheric pressure, in a mole ratio ofHNO₃ to salt of about 1.9:1 to about 2.5:1, until the dinitro derivativeof said aniline compound is formed and continuously removing saidderivative in said organic solvent from the third reaction zone, saidsubstituted aniline compound having the structural formula: ##STR4##wherein:R₇ is CH₃, C₂ H₅, C₃ H₇ --n, C₃ H₇ --i, .[.C₄ H₉ 13 i.]..Iadd.C₄ H₉ --i, .Iaddend.CF₃ or Cl; X is CH₃, --CH₂ --O--CH₃ or.[.--CH(CH₃)O--CH₃ .]. .Iadd.--CH(CH₃)--O--CH₃ .Iaddend.; and R₅ is C₃-C₇ secondary alkyl, or monochloralkyl C₃ -C₄.
 2. A process according toclaim 1, wherein said aniline compound is n-sec. butyl-3, 4-xylidine,N-(1-ethylpropyl)-3, 4-xylidine or N-(1-methylbutyl)-3, 4-xylidine. 3.The continuous process defined in claim 1, wherein, in the step in whichthe said dinitro derivative is formed, a spent nitric acid is yielded ina concentration of about 10%-50% HNO₃ by weight, characterized in thatthe said spent acid so yielded is thereafter used in the first definedsupplying step of said continuous process.
 4. A process of dinitrating adinitratable substituted aniline compound which comprises reacting (1)an aqueous nitric acid of about 10-40% HNO₃ by weight and substantiallyfree of sulphuric acid with (2) a substituted aniline compound in thepresence of a liquid, inert, water-immiscible organic solvent for saidaniline compound, in a mole ratio of about 1:1 to about 1:1.3 of HNO₃ tosaid aniline compound and at a temperature of about 40° to about 70° C.and atmospheric pressure, thereby forming an emulsion containing a saltof said nitric acid and aniline compound dissolved in said solvent,separating said emulsion into an aqueous phase and an organic phasecontaining said salt, separating the organic phase from the aqueousphase and reacting said salt in the organic phase with an aqueous nitricacid of 65-80% by weight HNO₃ and substantially free of sulphuric acidin a mole ratio of HNO₃ to said salt of about 1.9:1 to about 2.5:1 andat a temperature of about 40° C. to about 70° C. and at atmosphericpressures until a reactive mixture containing the dinitro derivative ofsaid compound is formed, said substituted aniline compound having thestructural formula: ##STR5## wherein: R₅ is C₃ -C₇ secondary alkyl ormonochloralkyl C₃ -C₄ ;X is CH₃, --CH₂ --O--CH₃ or --CH(CH₃)--O--CH₃ ;and R₇ is CH₃, C₂ H₅, C₃ H₇ --n, C₃ H₇ --i, C₄ H₉ --i, CF₃ or Cl.
 5. Aprocess according to claim 4, wherein said aniline compound is n-sec.butyl-3, 4-xylidine N-(1-ethylpropyl)-3, 4-xylidine, orN-(1-methylbutyl)-3, 4-xylidine.
 6. The process defined in claim 4wherein the reaction mixture containing said dinitro derivative alsocontains spent nitric acid in a concentration of 10%-50% HNO₃ by weight,together with the subsequent step of repeating said process utilizingthe said spent nitric acid in the said first-defined reacting step..Iadd.
 7. The process of dinitrating a dinitratable substituted phenolcompound without use of sulfuric acid which comprises the steps of:(A)supplying the following ingredients: an aqueous nitric acid of about 10%to 50% HNO₃ by weight and substantially free of sulfuric acid; adinitratable substituted phenol compound; and a liquid, inert,water-immiscible organic solvent for said substituted phenol compound;(B) reacting said ingredients, thereby forming an emulsion containing amononitrated derivative of the said compound; (C) permitting theseparation of said emulsion into an organic phase containing themononitrated derivative of said compound, and an aqueous phasecontaining aqueous spent nitric acid as a waste; (D) reacting saidseparated organic phase with aqueous nitric acid of 60% to 100% byweight HNO₃ and substantially free of sulfuric acid, thereby forming asecond mixture; (E) permitting the separation of said second mixtureinto an aqueous phase consisting of spent nitric acid of 10% to 50% byweight, and an organic phase containing the dinitrated derivative ofsaid substituted phenol compound; (F) removing said organic phasecontaining the dinitrated derivative, thus leaving the said spent nitricacid of step (E), and (G) repeating the foregoing steps (A) to (F),inclusive, utilizing as the acid in step (A) the said spent nitric acidof step (E), whereby the aqueous waste of step (C) is the only wastegenerated in the process..Iaddend. .Iadd.8. The process as defined inclaim 7, wherein the said spent nitric acid of step (E) is diluted tosubstantially 10% concentration prior to its utilization as the acid instep (A)..Iaddend. .Iadd.9. The process of dinitrating a dinitratableaniline compound without the use of sulfuric acid, which comprises thesteps of: (A) supplying the following ingredients: an aqueous nitricacid of about 10% to 50% HNO₃ by weight and substantially free ofsulfuric acid; a dinitratable aniline compound; and a liquid, inert,water-immiscible organic solvent for said aniline compound; (B) reactingsaid ingredients thereby forming an emulsion containing a mononitratedderivative of the said compound; (C) permitting the separation of saidemulsion into an organic phase containing the mononitrated derivative ofsaid compound and an aqueous phase containing aqueous spent nitric acidas a waste; (D) reacting said separated organic phase with aqueousnitric acid of 60% to 100% by weight HNO₃ and substantially free ofsulfuric acid, thereby forming a second mixture; (E) permitting theseparation of said second mixture into an aqueous phase consisting ofspent nitric acid of 10% to 50% by weight, and an organic phasecontaining the dinitrated derivative of said aniline compound; (F)removing said organic phase containing the dinitrated derivative, thusleaving the said spent nitric acid, and (G) repeating the foregoingsteps (A) to (F), inclusive utilizing as the acid in step (A) the saidspent nitric acid of step (E), whereby the aqueous waste of step (C) isthe only waste generated in the process..Iaddend. .Iadd.10. The processas defined in claim 9, wherein the residual nitric acid of the aqueousphase of said step (C) is substantially 10% by weight nitric acid orless..Iaddend.